1. Field
Apparatuses, devices, and articles of manufacture consistent with exemplary embodiments relate to a Fresnel lens and a pyroelectricity sensor module including the same.
2. Description of the Related Art
Pyroelectric infrared ray (PR) sensors are employed to detect human motion through detection of a change of infrared rays and are widely used in security fields, electric fields, home automation fields, or other industrial fields. The PR sensor is a pyroelectric device sensor configured to react to an infrared ray having a wavelength of about 10 μm emitted from a human body, and in general, the PIR sensor constitutes a pyroelectricity sensor module together with a signal processing board configured to control an output signal of the PIR sensor, and a condenser configured to concentrate light to the PIR sensor.
The PIR sensor typically uses a Fresnel lens as a condenser. The Fresnel lens is a lens configured of several ring-shaped lenses having a predetermined thickness to reduce a thickness of the lens. As the Fresnel lens, there are a single Fresnel lens having a single refractive index and a multi-Fresnel lens configured as a combination of stacked Fresnel lenses having different refractive indexes to secure a wider viewing angle. However, the multi-Fresnel lens suffers from a disadvantage in that a total size of a lens is increased in proportion to the number of stacked Fresnel lenses due to a space occupied by each of the Fresnel lenses. Accordingly, when the multi-Fresnel lens is applied as a condenser in the pyroelectricity sensor to secure a wider viewing angle, a size of the pyroelectricity sensor is also increased. This is not suitable for the recent trend of miniaturization of pyroelectricity sensors.